Hi, I'm stuck trying to trade my Chansey from FireRed to Pokémon Colosseum in order to get a Blissey that will wall any special teams in there, but every time I try to do it, Colosseum says that I cannot trade until I get to a further point in the game. The thing is, I've already completed all the Sevii Islands, I've beaten the Elite Four, obviously I've got all badges... So, what have I got to do?